Spacecraft for communications and broadcast services can operate in geosynchronous orbit. Such spacecraft can communicate with a subscriber terminal (ST) by generating a forward user downlink signal, also known as a service downlink beam, for reception by the ST associated with a user. In return, the ST can transmit back a return user uplink signal, also known as a service uplink beam, via the ST to the spacecraft. The positioning or pointing, of the forward user downlink signal towards the ST can drift over time, for example, due to temperature changes on the spacecraft, drifts in orbit, degradation of active components, etc.
Spacecraft that include a phase array antenna can use beamforming for transmitting the forward user downlink signal to an ST, and for receiving a return user uplink signal from an ST. Beamforming is a technique in which the phased array antenna is used to position the forward user downlink signal such that it is optimized in data capacity at a specific location of the user, and more specifically, the ST. Beamforming coefficients can be used to adjust the forward user downlink signal's gain and phase (e.g., by adjusting the gain of the signal provided by an amplifier) at the phased array transmitter to change the pointing of the signal. Exemplary beamforming coefficients include gain and phase coefficients, but are not limited thereto. Signal processing circuitry (e.g., including one or more beamformers and one or more digital channelizers, but not limited thereto) onboard the spacecraft can use the beamforming coefficients to “beamform” the forward user downlink signal by adjusting its gain and phase. However certain components of the spacecraft may need to be calibrated as the spacecraft drifts. Otherwise, beamformed signals may become degraded. Calibration of certain components of the spacecraft may also be needed even where beamforming is not performed onboard the spacecraft.